1. Field of Invention
The present invention relates to a backlight module. More particularly, the present invention relates to a light emitting diode.
2. Description of Related Art
A backlight module is one of the most important parts of a liquid crystal display (referred to as LCD). Since the liquid crystal is not a luminous body, the LCD panel is illuminated by the backlight module. The backlight module typically includes a light source, a light guide plate and many optical films such as, diffuser and reflector. Among all kinds of light sources of the backlight module, a light emitting diode (referred to as LED) has gradually become the most popular light source because of the high brightness, long lifetime, small size, and low energy consumption properties.
Nowadays, the luminous intensity of the LED has been improved, which means the desired luminance of the backlight module can be achieved with fewer LEDs. Fewer LEDs lowers the cost of the backlight module.
Please refer to FIG. 1A. FIG. 1A is a top view of a conventional backlight module 10, and FIG. 1A shows light distribution in a horizontal direction. When fewer LEDs 12 are used, the gap between LEDs 12 is wider. If the light field, or the light strength, in large angle of the light 16 emitted from the LED 12 is not enough to cover the wider gap, a dark strip 18 will be formed in the gap, and furthermore, non-uniform light may be provided to the LCD panel.
In addition, electronic devices are becoming thinner and lighter, so it is necessary to thin the LCD as well. Please refer to FIG. 1B. FIG. 1B is a side view of the conventional backlight module 10, and FIG. 1B shows light distribution in a vertical direction. As the LCD 12 becomes thinner, the backlight module 10 and the light guide plate 14 thereof also become thinner. When the thickness of the light guide plate 14 is almost as small as the thickness of the LED 12, the angular distribution of light field of the LED 12 in the vertical direction may be too broad and some of light 16 may leak out from the light guide plate 14, which may create light leakage problems.
Therefore, a new backlight module and a new LED thereof are necessary. The new LED may have different angular distribution of light field in different directions. In a horizontal direction, the light field should be enough at a large angle to prevent generating dark strips. In the vertical direction, the light field should be limited to small angles to ensure that each light beam is incidence on the light guide plate to prevent light leakage problems.